Combustion apparatus

ABSTRACT

A combustion apparatus for a regenerative gas turbine engine includes a combustion liner providing for prevaporization and premixing of fuel, for extended residence time after primary combustion, and for delayed dilution of the combustion products. The liner includes a premix-prevaporiation zone with relatively small cross-sectional area, with fuel injecting means at the upstream end. Air flows without swirl through this zone, and through a flare in the liner where the cross section area increases greatly into the combustion zone. A centerbody in the flare directs flow along the inner surface of the wall and additionally heats the fuel-air mixture. Supports for the centerbody define spaced chutes for the air entering the combustion apparatus, and vanes extending inwardly from the wall downstream of the flare deflect the flow from the chutes toward the center of the combustion zone. Combustion air is admitted only through the premix-prevaporization zone. The combuston zone and part of a residence zone downstream of the combustion zone are cooled by convection only, using dilution air. Entrance holes for dilution air are near the downstream end of the liner.

it tea atent [191 'Verdouw Dec.3, 1974 1 COMBUSTION APPARATUS [73]Assignee: General Motors Corporation,

Detroit, Mich.

[22] 'Filed: Apr. 12, 1973 [21] Appl. No.: 350,383

[52] US. Cl 611/3936, 60/39.65, 60/39.66, 60/39.7l, 60/39.72 R, 60/39.74R, 60/DIG. ll [51] lint. Cl F02c 3/06, F02c 7/22 [58] Field ofSearch..... 60/39.7l, 39.72 R, 39.74 R, 60/39.65, 39.66, 39.36

[56] g References Cited UNITED STATES PATENTS 2,424,765 7/1947 McCollum60/3965 2,614,384 10/1952 Feilden 60/39.66 X 2,679,137 5/1954 Probert60/39.72 R 2,959,006 11/1960 Ferric 60/3974 R 3,483,699 12/1969 Harvey60/39.74 R 3,535,875 10/1970 Sneeden et a1. 60/39.65 X 3,608,309 9/1971Hill et al. 60/39.65 3,618,319 11/1971 Kydd 60/39.65 X 3,643,431 2/1972Jamieson 60/39.71

Primary Examiner-C. J. Husar Assistant ExaminerRobert E. GarrettAttorney, Agent, or FirmPaul Fitzpatrick [57] ABSTRACT A combustionapparatus for a regenerative gas turbine engine includes a combustionliner providing for prevaporization and premixing of fuel, for extendedresidence time after primary combustion, and for delayed dilution of thecombustion products. The liner includes a premix-prevaporiation zonewith relatively small crosssectional area, with fuel injecting means atthe upstream end. Air flows without swirl through this zone, and througha flare in the liner where the cross section area increases greatly intothe combustion zone. A centerbody in the flare directs flow along theinner surface of the wall and additionally heats the fuel-air mixture.Supports for the centerbody define spaced chutes for the air enteringthe combustion apparatus, and vanes extending inwardly from the walldownstream of the flare deflect the flow from the chutes toward thecenter of the combustion zone. Combustion air is admitted only throughthe premix-prevaporization zone. The combuston zone and part of aresidence zone downstream of the combustionzone are cooled by convectiononly, using dilution air. Entrance holes for dilution air are near thedownstream end of the liner.

5 Claims, 3 Drawing Figures PATENTh B1B 3l974 SHEET 20F 2 COMBUSTIONAPPARATUS My invention is directed to combustion apparatus, particularlyto combustion apparatus for use at relatively high air inlettemperatures, and usually at considerable pressure, as contrasted tooperation near normal atmospheric conditions. Specifically, thepreferred embodiment of my invention is intended as a combustionapparatus for a regenerative gas turbine engine such as might be usedfor vehicle or aircraft propulsion.

Such engines operate at pressure ratios of the order of four orfive toone, which means that the pressure of the air in the combustionapparatus under sea level standard conditions rises to 45 to 60 psig. Ina nonregenerative engine, the air is heated to some extent by thecompression; in a regenerative engine, it is additionally heated by heattransfer from air exhausted from the engine, so that the air enteringthe combustion apparatus under full' power conditions may be at about900 F. Prior art combustion chambers for engines of this sort haveincorporated combustion liners within which the combustion takes place,and the principal emphasison design of such liners has been to securedependable burning of the fuel, minimize pressure drop, minimize thevolume of the combustion liner, and provide a durable and trouble-freestructure.

Because of the high temperatures and small combustion volume, suchcombustion apparatuses discharge substances regarded as'atmosphericpollutants. Such pollutants are principally particulates (normallyunburned carbon), carbon monoxide, unburned hydrocarbons, and nitrogenoxides resulting from the combination of atmospheric nitrogen and oxygenin the hot combustionzone.

Various expedie nts have been proposed and various combustion linerstructures have been designed in an effort to secure more completecombustion, thus a cleaner exhaust; and also to reduce as far asfeasible the generation of nitrogen oxides. t

The preferred combustion apparatus according to my invention involvesthe following'features to improve emission characteristics:

1. A premix-prevaporization section is provided up'- stream of theprimary combustion section to premix the fuel and primary 'air andto'preva'porize the fuel ahead ofthe combustion or reaction zone. Thisis to improve combustor homogeneity and to avoid fuel droplet burning,thereby eliminating carbon entirely.

2. The liner provides for sudden expansion from thepremix-prevaporization zone to the combustion zone for flamestabilization.

3. The primary combustion zone is operated somewhat lean to minimizeformation of oxides of nitrogen.

4. Dilution of the combustion products is delayed to provide arelatively extended residence of the combustion products for completeconsumption of carbon monoxide and hydrocarbons.

5. The combustion zone is cooled by convection cooling rather than filmcooling to avoid quenching of the combustion reactions in relativelycold film cooling air as in prior combustion liners.

While a liner according to the invention or including some of thefeatures of it may be employed in other types of installation, theconditions in a regenerative engine are favorable to it because therelatively higher temperature of the air entering the combustionapparaparatus before its entrance into the combustion zone;

to provide a combustion liner having a relatively great length betweenthe point of initiation of flame and the point of dilution or quenchingof the flame; to provide combustion apparatus in which a fuel-airmixture flows over a heated centerbody from a premix-prevaporizationzone of low cross-sectional area into a combustion zone of largecross-sectional area; and, in general, to provide combustion apparatusthat is better suited to the requirements of practice than those nowavailable.

The nature of my invention and its advantages will be clear to thoseskilled in the art from the succeeding detailed description of thepreferred embodiment of the invention and'the accompanying drawings. 7

FIG. 1 is a longitudinal sectional view of a combustion apparatusembodying the invention.

FIG. 2 is a cross-section view of the same taken on the plane indicatedby the line 2-2 in FIG. 1.

FIG. 3 is a cross-section view taken on the plane indicated by the line3-3 in FIG. 1.

The drawings represent the liner according to my invention as installedin combustion apparatus similar to that of the well known T63 aircraftengine, in which the combustion apparatus is of a single can type andthe single liner discharges-into an annular turbine inlet. In thatengine, compressed air issupplied to the combustion apparatus throughair tubes entering'the side of a combustion casing. It should beunderstood, however, that my invention is directed particularly to thestructure of the liner and to its cooperation with the combustionouter'casing and that various'types of combustion casings or air supplymeans may be used. Also, the liner need not have an annular outlet.Also, the principles of the invention may be embodied in an annularcombustion liner in which the liner is constituted by outer and innerwallshaving an annular combustion space betweenfthem.

Referring to FIG. 1, the combustion apparatus includes a casing 2adapted to receive air under pressure and a liner 3. The casing 2 isbolted at flanges 4 to an outer case 6 of the turbine of a gas turbineengine. As illustrated, the casing 2 includes a generally cylindricalportion extending in the upstream direction from the flanges 4 and anenlarged upstream portion 7 closed by an end cover 8. The combustion airis discharged through air tubes 10 into a plenum 11 defined by theupstream portion of the casing. The liner 3, which is of circularcross-section in the form illustrated, has a side wall 12 defining insuccession from the upstream end of the liner a primary or combustionair entrance 14, a generally cylindrical premix-prevaporization zone 15,a flare 16, a combustion zone 18, a residence zone 19, and a dilutionzone 20. The downstream end of the liner fits within an outer turbineshroud 22, and a flange 23 on the exterior of the downstream end of theliner fits over shroud 22. The liner is thus located at its downstreamor discharge end on the turbine outer shroud. An annular baffle 24mounted on the turbine defines with the shroud 22 an annular entrance 26into the turbine for the motive fluid generated in the combustionapparatus. A wall indicated schematically at 27 blocks flow of airthrough the gap between the casing and liner.

The upstream end of liner 3 is supported on a fuel injection ring 28disposed within the entrance 14 and supported by the fuel tubes 30 orother supporting means from a fitting 31 suitably fixed to the end cover8. Fuel is supplied to the combustion apparatus through a fuel tube 32.The combustion apparatus is designed for use with a liquid hydrocarbonfuel. The fuel injection ring 28 thus supports the upstream end of theliner.

The fuel injection ring, which is of known type, is considered to be themost suitable means for carburetting the air flowing into the inlet. Thefuel injection ring 28 is a composite circular ring defining an internalcircular manifold 34 for fuel supplied through tubes 30 and having ports35 extending from the manifold and directed tangentially to the interiorsurface of ring 28 to discharge fuel in the form of an annulus on theinner surface of the ring. This fuel is discharged behind a step orshoulder 36 on the interiorof the ring.

Four or more struts 38 extend from the exterior of ring 28 to the wallof the liner. Air under pressure flows from the plenum 11 over theexterior and through the interior of fuel injection ring 28 anddownstream through the premix-prevaporization zone 15. The fuel isairblast atomized off ring 28 by the air flowing past it. During travelthrough the premix-prevaporization zone, the heated air evaporates thefuel so as to provide a substantially homogeneous mixture of air andvaporized fuel. It should be noted that the struts 38 are not swirlers,and that the air preferably flows through the zone with nocircumferential component of velocity.

There is a transition from the premix-prevaporization zone 15 to thecombustion zone 18 through structure defined in part by the flare of theouter wall. There is an enlargement in area ofthe liner at this point ofabout 10 to one. 7 7

Flow through this transition zone is guided in part by a centerbody 39of circular cross section, the outer surfaceof which roughly parallelsthe inner surface of the liner wall. The centerbody is'hollow and isopen at'its downstream end so that heat from combustion in thecombustion zone heats the centerbody, thus contributing a slight amountof heat to the air-fuel mixture flowing over it. The centerbody issupported from the flaring wall portion 16 by eight generally V-shapedsheet metal struts or air guides 40 distributed around the circumferenceof the centerbody which may be welded to the centerbody and liner wall.These air guides define eight air chutes 42 between the struts. Thechute outlets occupy approximately half of the circumference of theannular passage 43 between the centerbody and the liner wall. Thecenterbody serves to deflect the flow of air and fuel along the insideof the wall 16 and the chutes concentrate this flow into eight jetsevenly distributed around the circumference. The centerbody and strutsare heated by the combustion just downstream of them and therefore theseheated bodies additionally heat the incoming air and fuel somewhat.

The centerbody 39 acts as a flow director. creating a turbulent zonebehind it to retain the flame against blowing out downstream of theliner. From the flare 16, the wall 12 of the liner continues firstcylindrical and then slightly diverging to the downstream end of theliner. A thorough mixing of the fuel and air in the combustion zone 18is promoted by a ring of eight turning vanes 44 welded to the wall, theform of which will be apparent from FIGS. 2 and 3. These deflect theincoming air-fuel mixture flowing through the chutes 42 toward the axisof the combustion liner and promote formation of a generally toroidalvortex flow and recirculation in the combustion zone to stabilizecombustion. The combustion occurs in the region near the flare l6 andvanes 44 and the resulting combustion products, in which the fuel isalmost entire burned, flow through the residence zone 19 toward thecombustion chamber outlet.

During the flow through the residence zone, time is allowed forcompletion of the reactions to reduce the remaining traces of unburnedfuel to a minimum.

In the combustion apparatus for a regenerative engine, as illustrated,approximately 40 percent of the total air supplied to the combustionapparatus enters through the air entrance l4 and constitutes combustionair. The remaining 60 percent is dilution air which flows radiallyinward from the casing through a ring of six large dilution air holes 46disposed near the downstream end of the liner. The space abreast ofthese holes and extending to the outlet of the liner constitutes thedilution zone 20.

The proportions of primary air and dilution air may, of course, bevaried to suit a particular installation.

The dilution air, before entering the liner through the holes 46, isused to cool the outer surface of the liner from the flare 16 downstreamby convection cooling, avoiding any introduction of air into the linerfor film cooling, for instance. Cooling is promoted by an annular shroud47 surrounding and spaced from the wall 12 of the downstream portion ofthe liner. The shroud 47 is mounted over; the wall 12 with freedom forrelative expansion of the parts by a structure including six plates 48extending radially outwardly from the inner 7 wall adjacent the flare 16and six similar plates 50 at the downstream end of the shroud 47. Theseplates are slidable in slots in the leading and trailing edges of theshroud 47 so the liner may expand radially relative to the coolershroud. Plates 48 may be welded to the liner before the shroud is put inplace andplates then may be inserted in the slots of the shroud andwelded to the liner wall. A ring of spacers 51 disposed around the outersurface of the liner wall 12 near the middle of the length of the shroudprevent distortion of this portion of the shroud from partially closingoff the annular flow passage 52 between the wall and shroud. A bafflering or blocking member 54 fixed to the outer surface of shroud 47extends across the gap between the shroud and the case 2 to minimize orcontrol flow over the outside of the shroud by-passing the cooling airpath 52. This blocking member may be considered to divide the spacewithin the casing into an upstream portion ahead of the blocking memberand a downstream portion surrounding the residence and dilution zones.

The operation of the combustion apparatus should be clear from theforegoing, but may be summarized briefly. Hot air under compressionordinarily on the order of four to five atmospheres and heated at about900 F. in the regenerator (at full power) is introduced into the plenuml1 and hydrocarbon fuel is introduced through pipe 32 into the annularfuel injection ring 28. The fuel is discharged circumferentially aroundthe inand then are quenched and diluted by the large quantity of airentering through dilution holes 46. The resulting mixture, which is of atemperature suitable for use in the turbine, is discharged through theannular outlet 26 into the turbine. The equivalence ratio in the primarysection of the specific liner described is calculated to be 0.73 underfull load conditions. This varies with load conditions, and variousfullload values may be adopted. There are reasons to believe a lowerequivalence ratio of the order of 0.5 at full load would provide betteremission characteristics.

ln'connection with combustion, it is recognized that not only theoverall equivalence ratio within the burning zone of the combustor, butalso local fuel-airratios at various points within the burning zone aresignificant. it is well known that as the fuel-air mixture becomesricher from a very low value, the curve of carbon monoxide emissionsdescends from a high value along a more or less hyperbolic curve to avery low value. Contrariwise, the emissions of nitrogen oxides are verylow when the fuel-air ratio is lean, but as the mixture becomesricherthe curve of nitrogen oxides begins to rise progressively moresteeply. With a rich mixture, the amount of nitrogen oxides produced isrelatively high. The best overa'll'emissions characteristic is obtainedat an intermediate value of fuel-air ratio. However, if the overallfuel-air ratio should beat the optimum point but there is poormixing,then there are both leaner and richer fuel-air mixture zoneswithin the combustion area. This causes deterioration in emissionperformance. I v i i g v 5 ln myc'ombustion apparatus described above,such uneve'n'distribution providing both locally lean and l0- cally richzones is prevented by turbulent diffusion of the fuel in the airwithi'nthe.premix prevaporization zone and by flow through the chutes 42. It isalso provided in the combustion zone by the structure impinging the jetsfrom the chutes 42 against the vanes 44 and recirculating the gaseswithin the combustion zone to achieve thorough mixing of the burning andunburned air-fuel mixtures.

For any given engine, it is possible to design the combustion apparatusso as to operate with the fuel-air ratio at the point where emissionsare at a minimum.

As pointed out above, the advantages of my combustion apparatus aregreatest where the incoming air is relatively hot. This is the case withnormal regenerative gas turbine engines. It also may be the case withvery high pressure ratio engines in which the work of compression raisesthe incoming air to relatively high temperatures. Also, in some cases,the combustion apparatus may work with air preheated otherwise than by aregenerator. In any event, the combustion chamber is particularlyeffective with air in the temperature range of 700 to 900 F. or above.

It will be seen that the apparatus described is well adapted to employthe modes of reduction of undesired contaminants outlined in theintroduction to this specification. It will also be seen that it is arelatively simple structure and, while larger than prior art combustionapparatus for such purposes, is not unduly bulky. Specifically, theliner, which is shown to scale in the drawing, is 15 inches long and 6%inches in diameter at its outlet.- it is about 6 inches longer than atypical prior art liner of similar capacity.

The detailed description of the preferred embodiment of the inventionfor the purpose of explaining its principles is not to be considered aslimiting or restricting the invention, as many modifications may be madeby the exercise of skill in the art.

I claim:

l. A combustion apparatus for a regenerative gas turbine engine or thelike comprising, in combination, a casing having an upstream portion anda downstream portion and having an entrance for hot compressed air inthe upstream portion; a combustion liner disposed within the casinghaving an upstream end in the upstream portion of the casing arid adownstream end in the downstream portion of the casing; the casing andliner defining between them a space for the compressed air discharginginto the liner, and the liner defining an outlet for combustion productsat its downstream end; the liner including wall means defining, in flowsequence from its upstream end, a premix-prevaporization zone, acombustion zone, and a dilution zone; the

premix-prevaporization zone having an open upstream end defining aprimary air inlet adapted to admit air flowing axially of the zonewithout significant circumferential velocity; means in the air inlet forcarburetting the air; the wall means defining a flare from thepremix-prevapo'rization zone into the combustion zone; a centerbodydisposed centrally of the flare effective to guide the flow along theinner surface of the wall means at the flare, the centerbody serving toheat additionally the carburetted air; the combustion zone being locatedimmediately downstream'of the flare and having subtrance holes throughthe wall means adjacent to the downstream end of the liner to admitdilution air from the downstream portion of the casing; and the linerwall means between the premix-preva'porization and dilution zones beingsubstantially imperforate.

2. A combustion apparatus for-a regenerative gas turbine engine or thelike comprising, in combination, a casing having an upstream portion anda downstream portion and having an entrance for hot compressed air inthe upstream portion; a combustion liner disposed within the casinghaving an upstream end in the upstream portion of the casing and adownstream end in the downstream portion of the casing; the casing andliner defining between them a space for the compressed air discharginginto the liner, and the liner defining an outlet for combustion productsat its downstream end;

the liner including wall means defining, in flow sequence from itsupstream end, a premix-prevaporization zone, a combustion zone, and adilution zone; the premix-prevaporization zone having an open upstreamend defining a primary air inlet adapted to admit air flowing axially ofthe zone without significant circumferential velocity; means in the airinlet for carburetting the air; the wall means defining a flare from thepremix-prevaporization zone into the combustion zone; a centerbodydisposed centrally of the flare effective to guide the flow along theinner surface of the wall means at the flare, the centerbody serving toheat additionally the carburetted air; guide means connecting thecenterbody to the wall means defining spaced chutes for the air andblocking flow between the chutes; the combustion zone being locatedimmediately downstream of the flare and having substantially greatercross-sectional area than the premix-prevaporization zone, and includingmeans effective to promote circulation and mixing in the combustionzone; shroud means spaced outwardly from the wall means extendingdownstream from the flare over the combustion zone effective to define ashallow flow path for convection cooling air over the exterior of thewall means; and blocking means between the shroud means and casingdisposed between the upstream and downstream portions of the casingeffective to direct a major portion of dilution air through the saidflow path; the dilution zone of the liner having dilution air entranceholes through the wall means adjacent to the downstream end of the linerto admit dilution air from the downstream portion of the casing; and theliner wall means between the premix-prevaporization and dilution zonesbeing substantially imperforate. I t

3. A combustion apparatus for a regenerative gas turbine engine or thelike comprising, in combination, a casing having an upstream portion anda downstream portion and having an entrance for hot compressed air inthe upstream portion; a combustion liner disposed within the casinghaving an upstream end in the upstream portion of the casing and adownstream end in the downstream portion of the casing; the casing andliner defining between them a space for the compressed air discharginginto the liner, and the liner defining an outlet for combustion productsat its downstream end; the liner including wall means defining, in flowsequence from its upstream end, a premix-prevaporization zone, acombustion zone, and a dilution zone; the premix-prevaporization zonehaving an open upstream end defining a primary air inlet adapted toadmit air flowing axially of the zone without significantcircumferential velocity; means in the air inlet for carburetting theair; the wall means defining a flare from the premix-prevaporizationzone into the combustion zone; a centerbody disposed centrally of theflare effective to guide the flow along the inner surface of the wallmeans at the flare, the centerbody serving to heat additionally thecarburetted air; guide means connecting the centerbody to the wall meansdefining spaced chutes for the air and blocking flow between the chutes;the combustion zone being located immediately downstream of the flareand having substantially greater cross-sectional area than thepremix-prevaporization zone, and including stirring vanes extending fromthe wall means into the path of flow from the chutes effective topromote circulation and mixing in the combustion zone; shroud meansspaced outwardly from the wall means extending downstream from the flareover the combustion zone effective to define a shallow flow path forconvection cooling air over the exterior of the wall means; and blockingmeans between the shroud means and easing disposed between the upstreamand downstream portions of the casing effective to direct a majorportion of dilution air through the said flow path; the dilution zone ofthe liner having dilution air entrance holes through the wall meansadjacent to the downstream end of the liner to admit dilution air fromthe downstream portion of the casing; and the liner wall means betweenthe premix-prevaporization and dilution zones being substantiallyimperforate.

4. A combustion apparatus for a regenerative gas turbine engine or thelike comprising, in combination, a casing having an upstream portion anda downstream portion and having an entrance for hot compressed air inthe upstream portion; a combustion liner disposed within the casinghaving an upstream end in the upstream portion of the casing and adownstream end in the downstream portion of the casing; the casing andliner defining between them a space for the compressed air discharginginto the liner, and the liner defining an outlet for combustion productsat its downstream end; the liner including wall means defining, in flowsequence from its upstream end, a premix-prevaporization zone, acombustion zone, a residence zone, and a dilution zone; thepremix-prevaporization zone having an open upstream end defining aprimary air inlet adapted to admit air flowing axially of the zonewithout significant circumferential velocity; means in the air inlet forcarburetting the air; the wall means defining a flare from thepremix-prevaporization zone into the combustion zone; a centerbodydisposed centrally of the flare effective to guide the flow along theinner surface of the wall means at the flare, the centerbody serving toheat additionally the carburetted air; the combustion zone being locatedimmediately downstream of the flare and having substantially greatercrosssectional area than the premix-prevaporization zone, and includingmeans effective to promote circulation and mixing in the combustionzone; shroud means spaced outwardly from the wall means extendingdownstream from the flare over the combustion zone effective to define ashallow flow path for convection cooling air over the exterior of thewall means; and blocking means between the shroud means and casingdisposed between the upstream and downstream portions of the casingeffective to direct a major portion of dilution air through the saidflow path; the dilution zone of the liner having dilution air entranceholes through the wall means adjacent to the downstream end of the linerto admit dilution air from the downstream portion of the casing; and theliner wall means at the combustion and residence zones beingsubstantially imperforate.

5. A combustion apparatus for a regenerative gas turbine engine or thelike comprising, in combination, a casing having an upstream portion anda downstream portion and having an entrance for hot compressed air inthe upstream portion; a combustion liner disposed within the casinghaving an upstream end in the upstream portion of the casing and adownstream end in the downstream portion of the casing; the casing andliner defining between them a space for the compressed air discharginginto the liner, and the liner defining an outlet for combustion productsat its downstream end;

the liner including wall means defining, in flow sequence from itsupstream end, a premix-prevaporization zone, a combustion zone, aresidence zone, and a dilution zone; the premix-prevaporization zonehaving an open'upstream end defining a primary air inlet adapted toadmit air flowing axially of the zone without significantcircumferential velocity; means in the air inlet for carburetting theair; the wall means defining a flare from the premix-prevaporizationzone into the combustion zone; a centerbody disposed centrally of theflare effective to guide the flow along the inner surface of the wallmeans at the flare, the centerbody serving to heat additionally thecarburetted air; guide means connecting the centerbody to the wall meansdefining spaced chutes for the air and blocking flow between the chutes;the combustion zone being located immediately downstream of the flareand having substantially greater cross-sectional area than thepremix-prevaporization zone, and including stirring vanes extending fromthe wall means into the path of flow from the chutes effective topromote circulation and mixing in the combustion zone; shroud meansspaced outwardly from the wall means extending downstream from the flareover the combustion zone effective to define a shallow flow path forconvection cool-' residence zones being substantially imperforate.

1. A combustion apparatus for a regenerative gas turbine engine or thelike comprising, in combination, a casing having an upstream portion anda downstream portion and having an entrance for hot compressed air inthe upstream portion; a combustion liner disposed within the casinghaving an upstream end in the upstream portion of the casing and adownstream end in the downstream portion of the casing; the casing andliner defining between them a space for the compressed air discharginginto the liner, and the liner defining an outlet for combustion productsat its downstream end; the liner including wall means defining, in flowsequence from its upstream end, a premix-prevaporization zone, acombustion zone, and a dilution zone; the premixprevaporization zonehaving an open upstream end defining a primary air inlet adapted toadmit air flowing axially of the zone without significantcircumferential velocity; means in the air inlet for carburetting theair; the wall means defining a flare from the premix-prevaporizationzone into the combustion zone; a centerbody disposed centrally of theflare effective to guide the flow along the inner surface of the wallmeans at the flare, the centerbody serving to heat additionally thecarburetted air; the combustion zone being located immediatelydownstream of the flare and having substantially greater crosssectionalarea than the premix-prevaporization zone, and including means effectiveto promote circulation and mixing in the combustion zone; shroud meansspaced outwardly from the wall means extending downstream from the flareover the combustion zone effective to define a shallow flow path forconvection cooling air over the exterior of the wall means; and blockingmeans between the shroud means and casing disposed between the upstreamand downstream portions of the casing effective to direct a majorportion of dilution air through the said flow path; the dilution zone ofthe liner having dilution air entrance holes through the wall meansadjacent to the downstream end of the liner to admit dilution air fromthe downstream portion of the casing; and the liner wall means betweenthe premixprevaporization and dilution zones being substantiallyimperforate.
 2. A combustion apparatus for a regenerative gas turbineengine or the like comprising, in combination, a casing having anupstream portion and a downstream portion and having an entrance for hotcompressed air in the upstream portion; a combustion liner disposedwithin the casing having an upstream end in the upstream portion of thecasing and a downstream end in the downstream portion of the casing; thecasing and liner defining between them a space for the compressed airdischarging into the liner, and the liner defining an outlet forcombustion products at its downstream end; the liner including wallmeans defining, in flow sequence from its upstream end, apremix-prevaporization zone, a combustion zone, and a dilution zone; thepremix-prevaporization zone having an open upstream end defining aprimary air inlet adapted to admit air flowing axially of the zonewithout significant circumferential velocity; means in the air inlet forcarburetting the air; the wall means defining a flare from thepremix-prevaporization zone into the combustion zone; a centerbodydisposed centrally of the flare effective to guide the flow along theinner surface of the wall means at the flare, the centerbody serving toheat additionally the carburetted air; guide means connecting thecenterbody to the wall means defining spaced chutes for the air andblocking flow between the chutes; the combustion zone being locatedimmediately downstream of the flare and having substantially greatercross-sectional area than the premix-prevaporization zone, and includingmeans effective to promote circulation and mixing in the combustionzone; shroud means spaced outwardly from thE wall means extendingdownstream from the flare over the combustion zone effective to define ashallow flow path for convection cooling air over the exterior of thewall means; and blocking means between the shroud means and casingdisposed between the upstream and downstream portions of the casingeffective to direct a major portion of dilution air through the saidflow path; the dilution zone of the liner having dilution air entranceholes through the wall means adjacent to the downstream end of the linerto admit dilution air from the downstream portion of the casing; and theliner wall means between the premix-prevaporization and dilution zonesbeing substantially imperforate.
 3. A combustion apparatus for aregenerative gas turbine engine or the like comprising, in combination,a casing having an upstream portion and a downstream portion and havingan entrance for hot compressed air in the upstream portion; a combustionliner disposed within the casing having an upstream end in the upstreamportion of the casing and a downstream end in the downstream portion ofthe casing; the casing and liner defining between them a space for thecompressed air discharging into the liner, and the liner defining anoutlet for combustion products at its downstream end; the linerincluding wall means defining, in flow sequence from its upstream end, apremix-prevaporization zone, a combustion zone, and a dilution zone; thepremix-prevaporization zone having an open upstream end defining aprimary air inlet adapted to admit air flowing axially of the zonewithout significant circumferential velocity; means in the air inlet forcarburetting the air; the wall means defining a flare from thepremix-prevaporization zone into the combustion zone; a centerbodydisposed centrally of the flare effective to guide the flow along theinner surface of the wall means at the flare, the centerbody serving toheat additionally the carburetted air; guide means connecting thecenterbody to the wall means defining spaced chutes for the air andblocking flow between the chutes; the combustion zone being locatedimmediately downstream of the flare and having substantially greatercross-sectional area than the premix-prevaporization zone, and includingstirring vanes extending from the wall means into the path of flow fromthe chutes effective to promote circulation and mixing in the combustionzone; shroud means spaced outwardly from the wall means extendingdownstream from the flare over the combustion zone effective to define ashallow flow path for convection cooling air over the exterior of thewall means; and blocking means between the shroud means and casingdisposed between the upstream and downstream portions of the casingeffective to direct a major portion of dilution air through the saidflow path; the dilution zone of the liner having dilution air entranceholes through the wall means adjacent to the downstream end of the linerto admit dilution air from the downstream portion of the casing; and theliner wall means between the premix-prevaporization and dilution zonesbeing substantially imperforate.
 4. A combustion apparatus for aregenerative gas turbine engine or the like comprising, in combination,a casing having an upstream portion and a downstream portion and havingan entrance for hot compressed air in the upstream portion; a combustionliner disposed within the casing having an upstream end in the upstreamportion of the casing and a downstream end in the downstream portion ofthe casing; the casing and liner defining between them a space for thecompressed air discharging into the liner, and the liner defining anoutlet for combustion products at its downstream end; the linerincluding wall means defining, in flow sequence from its upstream end, apremix-prevaporization zone, a combustion zone, a residence zone, and adilution zone; the premix-prevaporization zone having an open upstreamend defining a primary air inlet adapted to admit air flowing axially ofthe zone without significant circumferential velocity; means in the airinlet for carburetting the air; the wall means defining a flare from thepremix-prevaporization zone into the combustion zone; a centerbodydisposed centrally of the flare effective to guide the flow along theinner surface of the wall means at the flare, the centerbody serving toheat additionally the carburetted air; the combustion zone being locatedimmediately downstream of the flare and having substantially greatercross-sectional area than the premix-prevaporization zone, and includingmeans effective to promote circulation and mixing in the combustionzone; shroud means spaced outwardly from the wall means extendingdownstream from the flare over the combustion zone effective to define ashallow flow path for convection cooling air over the exterior of thewall means; and blocking means between the shroud means and casingdisposed between the upstream and downstream portions of the casingeffective to direct a major portion of dilution air through the saidflow path; the dilution zone of the liner having dilution air entranceholes through the wall means adjacent to the downstream end of the linerto admit dilution air from the downstream portion of the casing; and theliner wall means at the combustion and residence zones beingsubstantially imperforate.
 5. A combustion apparatus for a regenerativegas turbine engine or the like comprising, in combination, a casinghaving an upstream portion and a downstream portion and having anentrance for hot compressed air in the upstream portion; a combustionliner disposed within the casing having an upstream end in the upstreamportion of the casing and a downstream end in the downstream portion ofthe casing; the casing and liner defining between them a space for thecompressed air discharging into the liner, and the liner defining anoutlet for combustion products at its downstream end; the linerincluding wall means defining, in flow sequence from its upstream end, apremix-prevaporization zone, a combustion zone, a residence zone, and adilution zone; the premix-prevaporization zone having an open upstreamend defining a primary air inlet adapted to admit air flowing axially ofthe zone without significant circumferential velocity; means in the airinlet for carburetting the air; the wall means defining a flare from thepremix-prevaporization zone into the combustion zone; a centerbodydisposed centrally of the flare effective to guide the flow along theinner surface of the wall means at the flare, the centerbody serving toheat additionally the carburetted air; guide means connecting thecenterbody to the wall means defining spaced chutes for the air andblocking flow between the chutes; the combustion zone being locatedimmediately downstream of the flare and having substantially greatercross-sectional area than the premix-prevaporization zone, and includingstirring vanes extending from the wall means into the path of flow fromthe chutes effective to promote circulation and mixing in the combustionzone; shroud means spaced outwardly from the wall means extendingdownstream from the flare over the combustion zone effective to define ashallow flow path for convection cooling air over the exterior of thewall means; and blocking means between the shroud means and casingdisposed between the upstream and downstream portions of the casingeffective to direct the major portion of dilution air through the saidflow path; the dilution zone of the liner having dilution air entranceholes through the wall means adjacent to the downstream end of the linerto admit dilution air from the downstream portion of the casing; and theliner wall means at the combustion and residence zones beingsubstantially imperforate.